1. Field
A battery pack and a method of controlling charging and discharging of the battery pack capable of improving capacity and cycle life of a rechargeable lithium battery are provided.
2. Description of the Related Art
Batteries generate electrical power using an electrochemical reaction material for a positive electrode and a negative electrode. Rechargeable lithium batteries generate electrical energy due to chemical potential changes during intercalation/deintercalation of lithium ions at the positive and negative electrodes.
The rechargeable lithium batteries include a material reversibly intercalating or deintercalating lithium ions during charge and discharge reactions as both positive and negative active materials, and are filled with an organic electrolyte or a polymer electrolyte between the positive and negative electrodes.
As the positive active material for a rechargeable lithium battery, metal oxide composites such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (wherein 0<x<1), and LiMnO2 have been a focus of extensive research.
As for negative active materials of a rechargeable lithium battery, various carbon-containing materials capable of intercalating lithium ions (such as artificial graphite, natural graphite, and hard carbon) may be used. Since among the carbon-containing materials, graphite has a low discharge voltage of −0.2 Volts (V) relative to lithium, a battery including graphite as a negative active material has a high discharge voltage of 3.6 V to provide high energy density of a lithium battery, and also has improved reversibility to ensure a long life-cycle of a rechargeable lithium battery, and therefore, may be widely used. However, the graphite active material has low capacity in a view of energy density per unit weight of an electrode plate when the electrode plate is fabricated.
Recently, the high-capacity negative active material has been widely investigated to find a substitute for the graphite active material. One of these materials includes a silicon-containing active material such as silicon, a silicon-containing alloy, and the like. The silicon-containing active material has very high capacity compared to the carbon material but generates cracks due to a huge volume change when reacting with lithium during charge/discharge, breaking a silicon active material particle, such that the capacity is rapidly deteriorated leading to degradation of the cycle life according to repeating charge/discharge cycles.
Thus, there remains a need in a material which is capable of maintaining a desirable cycle life characteristics of the battery pack.